The present invention relates to a controller for rear brakes.
A conventional controller for the rear brakes of a heavy vehicle such as an autotruck and an autobus includes a fluid retarder and a proportioning valve. The controller functions so that the fluid retarder is caused to generate braking torque at the time of the descent of the vehicle on a downhill, the slowdown of the vehicle from a high speed, or the like, to prevent the braking force of each of the rear brakes from fading due to the rise in the temperature thereof, and to enhance the safety of the vehicle and lengthen the life of the friction material of the brakes. The proportioning valve supresses the rise in braking liquid pressure of the brakes to prevent the rear wheels of the vehicle from being locked undesirably to enhance the stability of the driving of the vehicle.
The conventional controller for the rear brakes acts to cause the fluid retarder and the proportioning valve function separately from each other and not to affect each other. For that reason, when the rear brakes are put into action as the fluid retarder remains in action, the braking torque of the rear brakes is added to that of the retarder to increase the total braking torque to the rear wheels of the vehicle to possibly undesirably lock the wheels. This is a problem, especially if proportioning valve is of the load-sensitive type in which a required level or braking at which the braking liquid pressure of the rear brakes begins to be controlled is changed depending on the load on the vehicle. During operation of a conventional load-sensitive type proportioning valve, the required level differs changed depending not only on whether the vehicle is loaded or unloaded but also on changes in conditions such as the rate of the deceleration of the vehicle, to cause the retarder to generate the braking torque and to simply add it to that of the rear brakes. For that reason, the rear wheels of the vehicle are made more likely to be undesirably locked prematurely.